(Phys.org) —In the growing area of flexible, transparent electronic devices, silicon has not played much of a role. Instead, materials such as indium tin oxide, carbon nanotubes, and others are often used ...

New catalysts designed and investigated by Tufts University School of Engineering researchers and collaborators from other university and national laboratories have the potential to greatly reduce processing costs in future ...

(Phys.org) —Chemical engineers at Stanford have designed a catalyst that could help produce vast quantities of pure hydrogen through electrolysis – the process of passing electricity through water to ...

(Phys.org) —Graphene quantum dots created at Rice University grab onto graphene platelets like barnacles attach themselves to the hull of a boat. But these dots enhance the properties of the mothership, ...

Researchers from the University of Houston and Trinity University have for the first time provided direct evidence of a water-mediated reaction mechanism for the catalytic oxidation of carbon monoxide.

(Phys.org) —Fuel cells are a promising, non-polluting way to power cars, but their platinum catalysts are so expensive that there's no way current technology could be economically scaled up for widespread ...

When chemist Tehshik Yoon looks out his office window, he sees a source of energy to drive chemical reactions. Plants "learned" to synthesize chemicals with sunlight eons ago; Yoon came to the field a bit ...

Generating electricity is not the only way to turn sunlight into energy we can use on demand. The sun can also drive reactions to create chemical fuels, such as hydrogen, that can in turn power cars, trucks ...

(Phys.org) —By directly comparing three closely related catalysts, scientists at the Center for Molecular Electrocatalysis established that hydrogen production speed and efficiency are influenced by the ...

(Phys.org) —Splitting water into its components, two parts hydrogen and one part oxygen, is an important first step in achieving carbon-neutral fuels to power our transportation infrastructure – including ...

Chemists have unexpectedly made two differently colored crystals – one orange, the other blue – from one chemical in the same flask while studying a special kind of molecular connection called an agostic ...

The ultrafast, ultrabright X-ray pulses of the Linac Coherent Light Source (LCLS) have enabled unprecedented views of a catalyst in action, an important step in the effort to develop cleaner and more efficient ...

Catalysis

Catalysis is the process in which the rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. The catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive catalysts. Catalysts that slow down the reaction are called negative catalysts or inhibitors. Substances that increase the activity of catalysts are called promoters and substances that deactivate catalysts are called catalytic poisons. For instance, in the reduction of ethyne to ethene, the catalyst is palladium (Pd) partly "poisoned" with lead(II) acetate (Pb(CH3COO)2). Without the deactivation of the catalyst, the ethene produced will be further reduced to ethane.

The general feature of catalysis is that the catalytic reaction has a lower rate-limiting free energy change to the transition state than the corresponding uncatalyzed reaction, resulting in a larger reaction rate at the same temperature. However, the mechanistic origin of catalysis is complex. Catalysts may affect the reaction environment favorably, e.g. acid catalysts for reactions of carbonyl compounds, form specific intermediates that are not produced naturally, such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause lysis of reagents to reactive forms, such as atomic hydrogen in catalytic hydrogenation.

Kinetically, catalytic reactions behave like typical chemical reactions, i.e. the reaction rate depends on the frequency of contact of the reactants in the rate-determining step. Usually, the catalyst participates in this slow step, and rates are limited by amount of catalyst. In heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. Analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts.

Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated or destroyed by secondary processes. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid-liquid system or evaporate in a solid-gas system.